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The CDC is asking U.S. health care professionals to maintain a high level of alert for the H7N9 virus, even though China has not reported any new cases since May 7 and the risk to Americans is small. CDC officials said the potential for a global pandemic is not yet known and physicians should consider H7N9 infection in patients with acute febrile respiratory illness and an appropriate travel or exposure history.

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A new study renews concerns that the H7N9 avian influenza virus that has killed 43 of 132 known patients in China could pose a serious pandemic threat. Chinese researchers report that one strain proved "highly transmissible" among ferrets. The species exhibits a similar response to influenza as humans and is considered a model for infection among people. "The findings suggest that only a few amino acid changes would be needed to make the avian H7N9 viruses highly transmissible," said virologist Chen Hualan.

The CDC is asking U.S. health care professionals to stay on high alert for the H7N9 virus, even though China has not reported any new cases since May 7 and the risk to Americans is small. CDC officials said the potential for a global pandemic is not yet known and physicians should consider H7N9 infection in patients with acute febrile respiratory illness and an appropriate travel or exposure history.

H7N9 fits two out of three criteria of a pandemic pathogen, according to physician Andrew Pavia of the University of Utah. He says the virus infects and causes disease in humans but seems to lack the ability to easily pass between them, although that could change as it mutates. If H7N9 does become easily transmissible between people, it has the potential to be worse than the 2003 H5N1 influenza outbreak. "Being worried doesn't do us any good; being prepared is what's important," said Pavia, emphasizing the need for monitoring and public health resources.

With four more human deaths in China, the death toll from H7N9 has reached 31, and 129 people have been infected since March, according to Chinese health officials. Transmission from poultry to humans has been confirmed. No evidence of human-to-human transmission exists, but 40% of infected people had no known direct exposure to poultry. According to the CDC, the current form of H7N9 will not cause a pandemic, but if it mutates, it could pose a serious global threat.

Escalating concerns about the H7N9 influenza strain that has surfaced in China have prompted scientists to use new technology to create a viral seed strain, potentially shortening the development time for a vaccine. The approach, developed after the 2009 H1N1 pandemic, uses the genetic code of the virus, instead of a sample of the virus itself, to create synthetic DNA and manufacture the virus then used in vaccine development. The time saved could be critical, said Robin Robinson, director of the Biomedical Advanced Research and Development Authority.